Many countries have highly developed systems for defense, especially for guarding their airspace against intruders or intrusions. This is necessary in addition to careful control of commercial and planned recreational traffic, which is managed by flight control in the area. In this case, any communication related to aircraft identification and flight plan is an initiative towards flight control, which will process the provided information before granting approval for the aircraft and planned route. This leads to identified and planned traffic in the airspace, where all the relevant communication channels can be used to control the traffic further. The control of other traffic, e.g. approaching unidentified aircraft, can be assumed to be a matter of national security, and is usually performed by military representatives or authorities.
Different radar systems can provide an image of unidentified traffic in the airspace, and serve military authorities in controlling approaching aircrafts also in neighboring airspace. The difference to commercial traffic is mainly in the method of creating an image, which relies on two-phase radars rather than signal received from transponders identifying the commercial aircraft. Radar systems are major investments, and can utilize multiple information sources to create an image of controlled airspace. There is also rather big difference in the utilization of resources under the normal state of readiness and elevated readiness (due to estimated or ongoing crisis). Therefore, a feasible utilization of resources can mean reduced control and image of the airspace, if there is no reason for elevated readiness (e.g. to populate multiple fixed or mobile radar stations for better coverage).